Ignition noise suppression center electrode assembly for spark plugs

ABSTRACT

An improved resistance element for suppressing random radio frequency radiation from the high voltage ignition circuit of an internal combustion engine. The resistance element is produced by sintering an extruded or compressed rod consisting essentially of copper oxides plus a heat destructible binder and from 0 to 10 percent of an inert plasticizer. The resulting element consists essentially of a combination of cupric oxide (CuO) and cuprous oxide (Cu2). Optional contact terminals may be formed on the element by applying a metallic coating to opposed ends of the capsule. The suppression element may be placed in the center electrode assembly of a spark plug electrically in series between a high voltage terminal and an electrode tip or at any suitable location in the high voltage ignition circuit for the internal combustion engine.

Rempes, Jr. et al.

[54] IGNITION NOISE SUPPRESSION CENTER ELECTRODE ASSEMBLY FOR SPARKPLUGS [75] Inventors: Paul E. Rempes, Jr., Royal Oak, Mich.; Le Roy H.Houghton, Toledo, Ohio [73] Assignee: Champion Spark Plug Company,

Toledo, Ohio [22] Filed: Aug. 20, 1971 [21] Appl. No.: 173,409

[52] U.S. Cl ..315/58, 313/136 [51] Int. Cl ..H 0lt 13/20 [58] Field ofSearch ..252/518; 315/58 [56] References Cited UNITED STATES PATENTS2,071,571 2/1937 Rabezzana et al ..3l5/58 2,633,521 3/1953 Becker et al."252/518 2,837,487 6/1958 Huttar ..252/5l8 1 June 5, 1973 PrimaryExaminerRoy Lake Assistant ExamjnerDarwin R. l-lostetter Att0rney-CarlF. Schaffer, Allen Owen, Henry K. Leonard et al.

57 ABSTRACT An improved resistance element for suppressing random radiofrequency radiation from the high voltage ignition circuit of aninternal combustion engine. The resistance element is produced bysintering an extruded or compressed rod consisting essentially of copperoxides plus a heat destructible binder and from 0 to 10 percent of aninert plasticizer. The resulting element consists essentially of acombination of cupric oxide (CuO) and cuprous oxide (Cu Optional contactterminals may be formed on the element by applying a metallic coating toopposed ends of the capsule. The suppression element may be placed inthe center electrode assembly of a spark plug electrically in seriesbetween a high voltage terminal and an electrode tip or at any suitablelocation in the high voltage ignition circuit for the internalcombustion engine.

10 Claims, 2 Drawing Figures IGNITION NOISE SUPPRESSION CENTER ELECTRODEASSEMBLY FOR SPARK PLUGS BACKGROUND OF THE INVENTION This inventionrelates to resistance elements and more particularly to an improvedresistance element for suppressing radio frequency radiation from thehigh voltage ignition circuit of an internal combustion engine.

The problem of eliminating radio frequency radiation from high voltageignition systems of internal combustion engines has been of increasingconcern in recent years because of its interference with the use of theradio channels for communications and for navigation. This problem hasbeen accentuated by the increasing number of automobiles, boats andaircraft and the simultaneous increase in the use of radio frequencyequipment in both communications and navigation.

The typical ignition system for an internal combustion engine includes aset of breaker points, a capacitor, an ignition coil, a spark plug, andconnecting wires. When the breaker points are closed, a battery isconnected to cause a current to flow in a primary winding of theignition coil, thereby establishing a magnetic field about, and storingenergy in, a ferrous core in the ignition coil. When the breaker pointsare opened, the magnetic field collapses to produce a high voltageacross a secondary winding of the ignition coil. The high voltage isapplied to, and arcs across, a spark gap in the spark plug, greatlydecreasing the impedance of the gap. The secondary coil winding and thelow impedance spark gap form a resonant circuit which oscillates as theenergy stored in the core is dissipated. The oscillations are in theradio frequency spectrum and may cause severe noise and interference inboth communications equipment and navigational equipment.

In the past, it has been found that random radio frequency radiationfrom the ignition system of internal combustion engines may be greatlyreduced or eliminated by placing a resistance element in the highvoltage ignition circuit for each spark plug. The resistance element maybe positioned in the bore of a spark plug insulator in series with thespark plug center electrode or it may be placed at some other convenientlocation in the ignition system, such as in a distributor rotor ordistributed in the high voltage ignition cables.

Prior art resistors, other than distributed resistances found inignition cables, are generally either of a carbon rod type, of a wirewound type, of a sintered resistive rod type or of a resistive massfired between glass seals in the center electrode bore through a sparkplug insulator. Each of the different types of resistors has advantagesand disadvantages. The carbon capsule resistor is, for example,relatively inexpensive compared to a wire wound resistor. However, whenthe carbon capsule resistor is placed in a spark plug and is heated toperhaps over 450F. or more during operation of the engine, the carbontendsto oxidize, resulting in an open circuit. For this reason, carbonresistors are not used in aircraft engines, which operate at highertemperatures than automobile engines and cannot tolerate a failure. Thecarbon resistor is also subject to failure since the resistance valuedepends upon how tightly the carbon particles are compacted and thermaland electrical stresses may loosen the particles, causing failure. Thewire wound resistor does not have as large a decrease in resistance athigher temperatures as carbon resistors and, therefore, is a much moreeffective suppressor. However, the wire wound resistor is expensivecompared to the carbon resistor and it presents problems both in arcingand in connecting terminals to the wire ends. Wire wound resistors arealso bulky and, therefore, difficult to use in smaller size spark plugs.

Resistance elements have also been formed directly in the centerelectrode bore in a spark plug insulator. One such type consists of aresistor formed by tamping a resistance composition in the bore of aspark plug insulator. Such compositions generally consist of aheterogenous mixture of a conducting or semi-conducting material, suchas carbon, metals, metal oxides, metal carbides, or combinationsthereof. The mixture is typically held in place by a pair of conductiveglass seals. In another embodiment, the resistance composition issuspended in a glassy matrix and the spark plug insulator is heated tofuse the composition into a solid resistor element.

SUMMARY OF THE INVENTION According to the instant invention, an improvedresistance element for suppressing random radio frequency radiation frominternal combustion engines is formed essentially from copper oxide. Thecopper oxide, a heat destructible binder and up to 10 percent by weightof a plasticizer are compressed, extruded or otherwise formed into a rodor capsule which is heated sufficiently to sinter the copper oxide intoa coherent resistance element and to simultaneously destroy the binder.The element may be provided with contact terminals by applying metalcoating to ends of the resistance element.

When the resistance element is heated to perhaps as high as 450F. ormore during operation of an internal combustion engine, the resistancevalue will fall to approximately 5 percent of the cold or roomtemperature resistance. In spite of this drastic decrease in resistance,the element is effective in suppressing radio frequency radiation fromignition systems in internal combustion engines. The drastic decrease inresistance as the resistor element is heated necessitates the use ofresistor elements having a significantly higher room temperatureresistance than is used with carbon resistors. The high cold resistanceresults in a high suppression during starting, when an engine mayproduce higher than normal radio frequency radiation. When theresistance element is heated during operation of the engine, theresistance drops into or below the normal resistance range forsuppressor resistors while maintaining its effectiveness as asuppressor. Copper oxide suppression elements having a cold resistanceon the order of 25,000 to 30,000 ohms and higher have been found to bemuch more effective than a 5,000 ohm carbon resistor and to be at leastas effective as a 5,000 ohm wire wound resistor at a lower cost and at asignificantly smaller size than a 5,000 ohm wire wound resistor.

Accordingly, it is the primary object of this invention to provide animproved resistance element for suppressing radio frequency radiationfrom ignition systerns in internal combustion engines.

Another object of the invention is to provide an improved spark plughaving an internal ignition noise suppression element formed essentiallyfrom copper oxide.

Other objects and advantages of the invention will become apparent fromthe following detailed description, reference being made to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view, inpartial section, of a spark plug including an internal noise suppressionelement constructed in accordance with the present invention; and

FIG. 2 is an enlarged section of one embodiment of a suppression elementconstructed in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, aconventional spark plug is shown with an internal resistor element 11for suppressing radio frequency radiation which may interfere withcommunications and navigational equipment. The spark plug 10 generallycomprises a tubular metal shell 12, an insulator 13 mounted in the shell12 and a center electrode assembly 14. The lower end of the shell 12 hasa threaded portion 15 for threadably engaging the head of an internalcombustion engine. A ground electrode 16 is welded to the lower end ofthe shell 12 for defining a spark gap with a center electrode tip 17.The center electrode assembly 14 is mounted in an axial bore 18extending through the insulator 13 and typically comprises the centerelectrode tip 17, a terminal 19, the suppression element 11, and aspring 20. The spring 20 is compressed either between the element 11 andthe electrode tip 17 or between the element 11 and the terminal 19 tomaintain a series electrical path between the terminal 19 and theelectrode tip 17.

According to the present invention, the suppression element 11 is formedfrom a composition consisting essentially of copper oxides. Particles ofcuprous oxide (Cu O) or a mixture of cuprous oxide and cupric oxide(CuO), having a size of less than 44 microns, and preferably an averagesize within the range of 6 to 13 microns, are formed into the desiredresistor shape and are heated for a sufficient time and at a sufficienttemperature to sinter into a coherent mass. A copper oxide mixturewithin a range of from 70 to lOO percent by weight of cuprous oxide and0 to percent by weight of cupric oxide has been found to produce asatisfactory ignition noise suppressor. A small quantity of heatdestructible binder, such as wax, starch, carboxycellulose, polyvinylalcohol, or natural and synthetic gums, may be added to the copper oxideparticles to maintain the desired resistor shape until the particles aresintered together. In a preferred embodiment, the binder ranges from 0.1to 4 percent. In addition, up to 10 percent of an inert plasticizer,such as bentonite, colloidal silica or ball clay, may also be added tothe copper oxide particles to increase the workability of the particlesas they are formed into the final shape of the suppression element.

The final composition of the finished suppression element 1] isdetermined by several factors, primarily the initial composition andparticle size of the copper oxides, the forming pressure, the firingtemperature, atmosphere and the firing time. If, for example, theinitial mixture comprises essentially cuprous oxide, the tinishedelement 11 may have a cored structure. During firing, oxygen fromsurrounding air combines with the cuprous oxide to form cupric oxide. Asshown in the vertical section through a cylindrical element 11 in FIG.2, a cupric oxide layer 21 is formed initially at the surfaces of theelement 11. A core portion 22 of the element 11 remains essentiallycuprous oxide, the composition of the starting mixture. The thickness ofthe outer cupric oxide layer 21 is determined by the firing time andtemperature. If the element 11 is fired for a sufficiently longperiod oftime at a sufficiently high temperature, the core 22 will disappear andthe element 11 will consist essentially of cupric oxide. It has beenfound, for example, that all of the cuprous oxide as indicated by X-raydiffraction in a 0.142 inch diameter element will be converted to cupricoxide if the element is heated to l550F. for 30 minutes, while onlyabout 20 percent of the cuprous oxide in a similar element was convertedto cupric oxide when the element was heated to 850F. for 30 minutes. Thecore 22 of the element 11 will, of course, include cupric oxide ifcupric oxide was present in the initial mixture from which the elementwas formed. In addition, when the element is heated to perhaps 1500F. ormore the bentonite plasticizer is dehydrated into aluminum silicate. However, the aluminum silicate is also essentially inert in the suppressionelement.

The actual resistance value of a copper oxide element is difficult tomeasure accurately due to the variable effect of contact resistance atboth ends of the element. Where a uniformity in measured resistance isdesired, conductive coatings may be placed on the ends of the element 11which contact the spring 20 and either the terminal 19 or the electrodetip 17 to form contact terminals. The coating reduces the likelihood ofhaving resistive contacts between the suppressor element 11 and eitherthe terminal 19 or the electrode tip 17 and the spring 20. The coatingis applied after the copper oxide particles are sintered into a coherentmass. The coating may, for example, consist of a silver powder suspendedin a resin or paste. The coating is applied onto the ends of theresistor and the element is tired at a sufficient temperature to fusethe silver to the ends of the sintered copper oxide element. However,when the suppressor element 11 is mounted in the center bore of a sparkplug and a voltage comparable to ignition voltage is impressed, contactresistance is negligible, making the conductive coating unnecessary. Thehigh voltage applied to the spark plug terminal 19 will arc across orbreak down any high resistance contact between the resistor element 11and either the terminal 19 or the electrode tip 17 or the spring 20.Such arcing does not affect or destroy the copper oxide element.

The suppression element may be shaped by any conventional method.However, in the preferred embodiments, the element is shaped either byextrusion or by pressing into a die. The preferred methods of formingthe resistance elements are described in detail in the followingexamples.

EXAMPLE I Resistance elements were formed by extrusion from a slipconsisting essentially of cuprous oxide particles plus a binder and aplasticizer. The cuprous oxide particles were of a commercial quality atleast percent pure and including free copper and cupric oxide asimpurities. The cuprous oxide particles were screened to a size lessthan 44 microns and having an average size within the range of 6 and 13microns. At least 0.1 percent and up to 4 percent by weight of a binderconsisting of approximately 15 percent fish glue and 85 percent glycerinand from 1 to percent by weight bentonite as a plasticizer were added tothe cuprous oxide particles. To this mixture, water was added toestablish a moisture content between 6 and percent. The mixture was thenpassed through a 0.140 inch die in a ram extruder and cut into rodshaving a length of approximately 0.25 inch. The cuprous oxide particleswere sintered into coherent rod shaped resistance elements by heating ina furnace for minutes at 1350F. The effects of contact resistancebetween the resistance elements and an external circuit were reduced bycoating the contact ends of the resistance element with a silver paste.The resistance elements were then refired at 1000F. to fuse the silverto the ends of the elements.

Typical resistance elements produced by the above example were evaluatedand showed that the elements had a resistance at room temperature of6500 ohms plus or minus 1500 ohms. When the resistor elements wereheated to a temperature within the normal operating range of 200F to450F., the resistance dropped to between 250 and 400 ohms, or about 5percent of the room temperature resistance.

EXAMPLE II Resistance elements were pressed from a mixture comprisingessentially pure cuprous oxide particles including nor more than 5percent impurities, 2 percent by weight of a paraffin binder and 1percent by weight of bentonite as a plasticizer and a suspension agent.Prior to pressing, the mixture was formed into spherically shapedpellets of a 200 micron nominal size by a conventional spray dryingprocess to enhance the flow properties of the mixture. The sphericalpellets were then placed in a die, where they were pressed at pressuresbetween 5 and tons per square inch to form resistance elements having adiameter of 0.140 inch and a length of approximately 0.25 inch. As inExample I, the resistance elements were heated for 30 minutes at 1350F.to sinter the cuprous oxide particles and simultaneously to burn out thebinder.

Typical resistance elements produced by the above example were evaluatedand again showed a resistance at room temperature in the range of 6500ohms plus or minus 1500 ohms. At an operating temperature within therange of 200F. to 450F. the resistance dropped to approximately 5percent of the room temperature resistance.

For suppressing radio frequency radiation from the ignition system of aninternal combustion engine with the efficiency of a 5000 ohm wire woundresistor, sintered copper oxide elements having at least a 25,000

ohm room temperature resistance were formed for placement in series inthe center electrode of a spark plug. When the spark plug insulator andthe internal resistor were heated to an operating temperature range ofapproximately 200F. to 450F., the resistance value dropped to about 5percent of the cold value, or to about 1250 ohms or more depending uponthe cold temperature resistance. The resistance elements were effectiveas ignition noise suppressors at the lower resistance value.

EXAMPLE Ill Several different suppression elements were formed fromessentially cuprous oxide and from mixtures comprising essentiallycuprous oxide and up to 30 percent by weight cupric oxide. The cuprousoxide particles of 10 microns. In each case, 1 percent by weightbentonite was added as an inert plasticizer and 2 percent by weightpolyvinyl alcohol was added as a temporary binder. The elements werepressed at from 15 to 47.5 tons per square inch into cylinders having a0.142 inch diameter and a 0.250 inch length and were then sintered byfiring first at 850F. for a 30 minute soak and then at 1500F. for a 6minute soak.

In analyzing the sintered elements, bulk resistances were found to rangefrom 30,000 ohms to 120,000 ohms, as measured by a 500 volt megger witha 20 pound terminal pressure applied at opposite ends of each cylinder.When the elements were placed in center electrode assemblies in sparkplugs and operated in internal combustion engines, they were found to beat least comparable in efficiency to 5000 ohm wire wound resistors forsuppressing ignition noise. The efficiency of the various elements assuppressors and the resistances of the elements did not appear to berelated to the final composition of the elements. An X-ray analysisindicated that the overall composition of the finished elements rangedfrom a 50:50 mole ratio to a :30 mole ratio of cuprous oxide to cupricoxide. The final composition was affected by the forming pressure. Afirst group of elements formed from essentially percent cuprous oxideand pressed at 15 tons per square inch showed a cuprous oxide to cupricoxide mole ratio of 54:36, while a second group of elements formed fromthe same initial mixture and pressed at 25 tons per square inch had amole ratio of 63:37 and a third group of elements formed from the sameinitial mixture and pressed at 42 tons per square inch had a mole ratioof 70:30. The forming pressure also affected the mechanical strength ofthe finished elements. For the above three groups of elements, theelements formed at 15 tons per square inch were crushed by axial loadsof about 41 pounds; the elements formed at 25 tons per square inch werecrushed by axial loads of about 50 pounds; and the elements formed at 42tons per square inch were crushed by axial loads of about 64 pounds.

EXAMPLE lV Two groups of elements were formed essentially from cuprousoxide particles having an average diameter of 6 microns. To theparticles, 1 percent by weight bentonite and 2 percent by weightpolyvinyl alcohol were added as a plasticizer and as a temporary binder,respectively. This mixture was then formed into spherical pellets havinga 200 micron nominal size. The elements were formed into 0.142 inchdiameter cylinders 0.250 inch long by pressing at 15 tons per squareinch. The first group was heated to 1500F. for a 6 minute soak and thesecond group was heated to 1500F. for a 30 minute soak.

An analysis of the elements showed that elements in the first group hada cold resistance on the order of 300,000 ohms and elements in thesecond group had a cold resistance on the order of 50,000 to 55,000ohms. Elements in both groups were comparable to 5000 ohm wire woundresistors for suppressing ignition noise from internal combustionengines when installed in center electrode assemblies of spark plugs. AnX-ray analysis also showed that the overall composition of elements inthe first group consisted essentially of copper oxide having a moleratio of 20:80 of cuprous oxide to cupric oxide. Elements in the secondgroup were essentially 100 percent cupric oxide, plus aluminum silicatefrom the dehydrated bentonite. Stronger mechanical binding resulted fromthe longer heating in the second group. An average axial force of 66pounds was required to crush elements in the second group, while anaverage axial force of only 52 pounds was required to crush elements inthe first group.

The sintered copper oxide suppressor element has several unexplainableproperties. It has been found that many resistance materials that have adrop in resistance similar to sintered copper oxides are ineffective assuppressors. For example, a barium ferrite resistor having the sameresistance under operating conditions did not function as a radiofrequency noise suppressor. It has also been found that the suppressioncharacteristics of sintered copper oxide elements appear to benonlinear, as measured with a low voltage. In other words, a 30,000 ohm(cold) resistor may not be as effective as either a 20,000 ohm (cold) ora 40,000 ohm resistor (also cold). The reason for the apparentnon-linearity has not yet been explained. The apparent non-linearitymay, however, result from a difficulty in taking accurate low voltageresistance measurements of the copper oxide elements.

Suppression elements have also been integrally formed in spark pluginsulators by compacting mixtures consisting essentially of copper oxideinto the center electrode bore and firing the insulator. Since theinsulator prevents oxygen in the air from contacting the mixture duringfiring, cuprous oxide is not converted to cupric oxide during firing. Asa result of this, better results have been obtained by using cupricoxide or a mixture of cupric oxide and cuprous oxide as a startingmaterial. However, cupric oxide alone is difficult to sinter and higherfiring temperatures and longer firing times may be required, forexample, firing from minutes to 2 hours at 1500F. to l800F.

It will be appreciated that various modifications and changes may bemade in the method of producing a sintered copper oxide ignition noisesuppression element and in the use of such an element without departingfrom the spirit and the scope of the claimed invention.

What we claim is:

l. in a spark plug for an internal combustion engine including a hollowtubular shell and an insulator positioned within the shell, saidinsulator having a bore for holding a center electrode assembly, animproved center electrode assembly comprising, in combination, a firingtip, a terminal, an ignition noise suppression element comprising asintered mass consisting essentially of copper oxide, and meansconnecting said sintered copper oxide mass electrically in seriesbetween said tip and said terminal.

2. An improved center electrode assembly for a spark plug, as defined inclaim 1, wherein said sintered mass of copper oxide has a cylindricalshape with opposed ends for electrically connecting to said tip and saidterminal.

3. An improved center electrode assembly for a spark plug, as defined inclaim 2, wherein said connecting means includes electrically conductivecoatings on said opposed ends of said cylindrical shaped mass of copperoxide.

4. An improved center electrode assembly for a spark plug, as defined inclaim 3, wherein said conductive coating is of silver.

5. The improved center electrode assembly for a spark plug, as definedin claim 1, wherein said sintered mass includes up to 10 percent of aninert plasticizer.

6. An improved center electrode assembly for a spark plug, as defined inclaim 5, wherein said plasticizer is bentonite.

7. An improved center electrode assembly for a spark plug, as defined inclaim 1, wherein said connecting means comprises a spring, said springbeing compressed between said sintered copper oxide mass and one of saidtip and said terminal.

8. An improved center electrode assembly for a spark plug, as defined inclaim 1, wherein said sintered mass consists essentially of cupricoxide.

9. An improved center electrode assembly for a spark plug, as defined inclaim 1, wherein said sintered mass consists essentially of cuprousoxide and cupric oxide.

10. An improved center electrode assembly for a spark plug, as definedin claim 9, wherein the surfaces of said sintered mass are essentiallycupric oxide and a core portion of said sintered mass is essentiallycuprous oxide.

2. An improved center electrode assembly for a spark plug, as defined inclaim 1, wherein said sintered mass of copper oxide has a cylindricalshape with opposed ends for electrically connecting to said tip and saidterminal.
 3. An improved center electrode assembly for a spark plug, asdefined in claim 2, wherein said connecting means includes electricallyconductive coatings on said opposed ends of said cylindrical shaped massof copper oxide.
 4. An improved center electrode assembly for a sparkplug, as defined in claim 3, wherein said conductive coating is ofsilver.
 5. The improved center electrode assembly for a spark plug, asdefined in claim 1, wherein said sintered mass includes up to 10 percentof an inert plasticizer.
 6. An improved center electrode assembly for aspark plug, as defined in claim 5, wherein said plasticizer isbentonite.
 7. An improved center electrode assembly for a spark plug, asdefined in claim 1, wherein said connecting means comprises a spring,said spring being compressed between said sintered copper oxide mass andone of said tip and said terminal.
 8. An improved center electrodeassembly for a spark plug, as defined in claim 1, wherein said sinteredmass consists essentially of cupric oxide.
 9. An improved centerelectrode assembly for a spark plug, as defined in claim 1, wherein saidsintered mass consists essentially of cuprous oxide and cupric oxide.10. An improved center electrode assembly for a spark plug, as definedin claim 9, wherein the surfaces of said sintered mass are essentiallycupric oxide and a core portion of said sintered mass is essentiallycuprous oxide.